The present invention relates to production of high performance solid electrolyte capacitors and affords a quality control method to enhance reliability of testing to thereby increase quality of end products and reduce production costs compared to state-of-the-art.
The well known processing of solid electrolyte capacitors involves production of powders from tantalum (substitutable in some cases by like reactive metals, e.g., titanium, niobium, tantalum-niobium alloys) of certain capacitance, voltage breakdown (VBD) and leakage values. The powders are made into porous anode blocks by powder metallurgy techniques; anodic oxide is "formed" on exposed powder surfaces within the porous anode mass by wet electrochemistry methods; the formed anodes are tested for capacitance, VBD and leakage in a wet electrochemical capacitor simulating arrangement; the anodes are further processed by impregnation with a liquid form solid electrolyte precursor and hardening the precursor to a solid form (typically by pyrolysis); followed by applying a counter-electrode (cathode); packaging; and preliminary testing and life testing, on a sample basis, of the finished capacitors. The impregnation and pyrolysis process is applied as a number of subdivided steps of impregnation and pyrolysis. During the course of these steps, it may be necessary to reform the anodic oxide.
It has been long known that the process of introducing a solid electrolyte into the formed anode can be somewhat destructive to the anodic oxide film. That is why the anodes are periodically reformed during the solid capacitor process as a means of repair of such damage. Ultimately, the damage to the oxide film is quite extensive despite the periodic repairs. That is why solid capacitors must be derated by some 67-75%, i.e. rated at 25-33% of their formation voltage (i.e. voltage rating at 25-33% of formation voltage) vs. 50-70% net rating in wet electrolyte capacitors.
It is a principal object of the present invention to provide a test process that provides a reliable indicator of eventual VBD and leakage performance in advance of life testing to identify anodes especially degraded in the course of impregnation-pyrolysis and avoid final processing and life test of these while processing and life testing anodes which are likely to perform well in eventual life testing and ultimate usage.